[mkgmap-dev] Weird MultiPolygon intersection warning

Mon Feb 1 21:59:47 GMT 2010

> That's what I suspected.  Would it be feasible to process the multipolygons
> before converting to mkgmap coordinates?
I don't know but I think it's not possible.

> Or how hard would it be to process
> multipolygons that contain intersecting lines?

You have to differ between "self-intersecting", "intersecting" and 
"overlapping" lines.
Self-intersecting lines usually (not in your case) point to problematic 
OSM data. So the warning is a warning which points to potientially wrong 
data. But the lines are processed by mp.

If you have intersecting lines the mp code cannot decide which polygon 
is contained by another polygon. From my point of view this cannot be 
fixed without major drawbacks.

Overlapping lines are not allowed for multipolygons but are sometimes 
used in OSM data. One could debate if they should be allowed or not but 
in the end they exist. To detect overlapping lines the mp code must be 
changed. At the moment I don't have a good and performant algorithm to 
do that, so I cannot say for sure if that's possible or not.

WanMil